Technical Field
The present invention relates to the technical field of sewage treatment, more specifically to a method for advanced treatment of bio-treated coking wastewater.
Description of Related Art
Coking wastewater is generated in the high-temperature carbonization of raw coal, coal gas purification and refining process of chemical products. The constituents in coking wastewater vary greatly in accordance with the nature of raw coal, carbonization temperature and recovering modes of chemical byproducts. Coking wastewater usually contains ammonia nitrogen, cyanides, thiocyanides, phenols and other pollutants such as polycyclic aromatic hydrocarbons and heterocyclic compounds containing nitrogen, oxygen and sulfur. These persistent pollutants are very harmful to the ecological system, in addition, most of polycyclic and heterocyclic compounds are subject to constant transformation and are carcinogenic by nature. Therefore, treatment of coking wastewater is a tough challenge for all countries. At present, most coking plants discharge coking wastewater after such processes as de-phenol pretreatment and biological treatment, the biological oxygen demand (BOD) in the effluent treated in this way can reach the B-level of [Chinese National] Integrated Wastewater Discharge Standard (GB8978-1996), but the chromaticity and the chemical oxygen demand (COD) therein usually exceed the national standards. Though advanced oxidation processes and active carbon adsorption can effectively solve the above problems, they are limited in use due to high operating cost and small treatment capacity. Thus, seeking a simple, low-cost and effect-stable technology for the advanced treatment of coking wastewater becomes a primary yet challenging task.
In recent years, iron oxide and manganese oxide are widely used in removing heavy metals (Zn, Cd, Ni, Pb, etc.) and inorganic ion pollutants (arsenate, fluorinion, perchlorate, etc.) in solution, which have been reported in various literature and patents. Some organics in the wastewater can form coordinated complexes with hydrated ferric oxide and hydrated manganese oxide, which makes it possible to remove organic pollutants from coking wastewater by means of nano-composite adsorbents made of iron oxide or manganese oxide. However, up-to-standard discharge of coking wastewater that has been treated as such is still a technical difficulty.